1. Field of the Invention
The present invention relates to a clutch system comprising a clutch device, in particular for arrangement in a drive train between a drive unit and a transmission, and comprising an actuating device for actuating the clutch device hydraulically by means of at least one hydraulic slave cylinder, the actuating device having a hydraulic-medium supply device for supplying pressurized hydraulic medium and a valve arrangement which can be used to feed hydraulic medium to the slave cylinder and discharge hydraulic medium from the slave cylinder.
2. Description of the Related Art
It is appropriate to design the valve arrangement with at least one proportional valve which is used for controlling/regulating the inflow of hydraulic medium into the slave cylinder and for controlling/regulating the discharge of hydraulic medium from the slave cylinder, since proportional valves are available which permit very precise metering of the hydraulic medium flowing into the slave cylinder and of the hydraulic medium flowing out of the slave cylinder and, accordingly, the clutch device can be actuated very sensitively with the effect of releasing or engaging it. Conventional automated clutch systems, for example, have thus been actuated by proportional and directional pressure-regulating valves.
However, proportional and directional pressure-regulating valves have to be manufactured keeping to exacting tolerances and are therefore comparatively costly. Furthermore, the leakage and control oil losses in the majority of proportional valves or servo valves are relatively high. If the clutch is to remain actuated (engaged in the case of a clutch of the NORMALLY OPEN type or released in the case of a clutch of the NORMALLY CLOSED type), the hydraulic-medium supply device, which generally has a hydraulic pump, has to accordingly continuously maintain a certain pressure level.
Another aspect is the ventilation of the hydraulic system, in particular of the hydraulic slave cylinder of the clutch system. Conventional clutch systems with a master cylinder which can be actuated by the clutch pedal have been ventilated by repeated actuation of the clutch pedal. Another possibility is to make the clutch system operationally ready by using a vacuum filling device. A vacuum filling device of this type will be required, in particular, for conventional clutch systems, in particular wet-running clutch systems, without a clutch pedal. However, a vacuum filling device of this type is relatively expensive and will not be able to be kept at hand by all garages. The conventional ventilation by repeated actuation of the clutch pedal, if this ventilation possibility is still provided at all, is also disadvantageous at least to the extent that it requires a comparatively large amount of time and, in practice, carelessness by the operator may cause errors to occur, with the slave cylinder not being completely ventilated.